1. Field of the Invention
This invention relates to a semiconductor wafer and a process for manufacturing a semiconductor device, particularly to a process for dividing a semiconductor wafer into separate semiconductor chips by dicing and a semiconductor wafer used for the process.
2. Description of the Related Art
Conventionally, a semiconductor chip has been manufactured as follows. First, a plurality of semiconductor chips 2 are formed on a semiconductor wafer 1 (FIG. 1). Then, along scribe lines 3 between the areas with a semiconductor chip 2, the semiconductor wafer 1 is cut with a cutter known as a dicing blade. Thus, the blade-cut areas 13 are formed to divide the wafer into separate semiconductor chips 12 (FIG. 4). Such a process for dividing a water into separate semiconductor chips 12 is generally called dicing.
For diving, it is necessary that the dicing blade cuts the semiconductor wafer 1 precisely along the scribe line 3. Therefore, as shown in FIG. 2, an alignment mark 41 is formed on the scribe line 3 for aligning the dicing blade using the alignment mark 41 as a guide mark. The alignment mark 41 may be made of a metal film, where a difference in a reflectance is generated between the semiconductor wafer 1 and the metal alignment mark 41. Thus, a position of the alignment mark 41 can be checked by the difference in a reflectance, allowing the dicing blade to be aligned. Such technique has been disclosed in, for example, Laid-open patent publication No. 1989-304721.
In addition, there may be formed a TEG (Test Element Group) 42 on the scribe line 3, which may contain a metal. Such technique has been disclosed in, for example, laid-open patent publication No. 2002-176140.
Recently, a semiconductor chip has been significantly size-reduced. Size reduction in a semiconductor chip increases the number of semiconductor devices obtained from a piece of semiconductor wafer. However, when a scribe line has the same width as that of a scribe line in a conventional semiconductor wafer, a proportion of the scribe line is increased in an area on the semiconductor wafer. Therefore a width of a scribe line must be reduced for further increasing the number of semiconductor chips obtained from a piece of semiconductor wafer.
However, when a scribe line has a shorter width than that in a conventional semiconductor wafer, chipping during dicing may cause damage in a semiconductor chip. In particular, an interlayer insulating film formed on a semiconductor wafer is more fragile than the semiconductor wafer itself, so that chipping in an interlayer insulating film on a scribe line probably reaches an interlayer insulating film in a semiconductor chip area.
Thus, as shown in FIG. 3, there has developed technique that a scribe line 3 is irradiated with a laser beam to remove an interlayer insulating film in the scribe line 3 in advance, before cutting with a dicing blade. This technique has been disclosed in, for example, Laid-open patent publication No. 2003-320466. Using this technique, a laser irradiation area 10 is formed in the scribe line 3. Since the area does not have an interlayer insulating film, chipping in an interlayer insulating film on an scribe line can be avoid during cutting with a dicing blade. Therefore, chipping never reaches an area in which a semiconductor chip is formed.
Laid-open patent publication No. 1988-250119 has described means for maximizing the number of semiconductor chips obtained from a piece of semiconductor wafer. Specifically, there has been disclosed a semiconductor wafer where in a strip type semiconductor chip, a scribe line between shorter edges has a shorter width than that of a scribe line between longer edges and an accessory pattern is formed on the scribe line between shorter edges (See, FIG. 2 therein).